Pump flow rate
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The plant has a pump with a capacity of 150 cubic meters per hour; the pipe diameter is Dn200, and this pipe splits into three Dn80 branches that supply water to three cooling water heat exchangers located at different distances from each other. Each heat exchanger requires a flow rate of 35 cubic meters per hour. The heat exchanger that is closest, at a distance of about 30 meters, is not in use. For the heat exchanger that is second closest, located 90 meters away, the measured flow rate is 45 cubic meters per hour. As for the farthest heat exchanger, located 200 meters away, the measured flow rate is only 20 cubic meters per hour. Although there is pressure loss in the pipes, the pump still has a large surplus in flow capacity. Should the pump’s output be increased to match the flow rate required by the farthest heat exchanger, with an corresponding increase in flow rate for the heat exchanger that is second closest? Is it still because the branch flow rate for DN80 cannot be increased, and based on the principle of equal pressure drop, the third heat exchanger can only have such a low flow rate? What other solutions are there?
Throttling, regulating flow rate. First, ensure the flow rate to the farthest system, then adjust the opening to maintain the flow rate of the second pump. 40 m3 is guaranteed; a DN80 pipe diameter is almost the limit!
The pump parameters represent just a point on the curve; actual operation at that point relies on adjustment by the piping system
If the pipe diameter is increased, is it possible for the flow rate to increase?
If the owner wants a second heat exchanger without reducing the flow rate, are there any other options? By increasing the pipe diameter to 100, can we increase the flow rate in the third heat exchanger?
Judging from the current situation, increasing the pipe diameter is likely to have little effect. The flow rate in the second heat exchanger isn’t very high either; by increasing the pipe diameter, the flow rate in the third heat exchanger might increase a bit, but as the flow rate rises, the pressure will drop. The flow rate in the second heat exchanger might decrease somewhat. It’s best to do some calculations to find out for sure. However, the flow rates measured on-site may not be accurate; it’s necessary to consider the actual operating pressure and current of the pump, and compare them with the test curves to determine the actual operating conditions
I’m not sure whether your process is part of the original design or something that was created through subsequent modifications. If it is the former, it is a problem of operational control. If it’s the latter, it may be related to the design. Let’s talk about the operation method. Typical control involves regulating the cooling water flow at the outlet of the coolers in each branch, or controlling the balanced distribution of water flow as needed. The load on the water pump should ideally be operated at full capacity by maximizing the motor’s rated current. The rated current indicates the maximum flow rate, and it can also be used to determine whether the water pump meets its performance requirements. For reference.